Many data communication systems utilize high performance data cables having at least four twisted pairs. Typically, two of the twisted pairs transmit data and two of the pairs receive data. A twisted pair is a pair of conductors twisted about each other. A transmitting twisted pair and a receiving twisted pair often form a subgroup in a cable having four twisted pairs.
A high performance data cable utilizing twisted pair technology must meet exacting specifications with regard to data speed and electrical characteristics. The electrical characteristics include such things as controlled impedance, controlled near-end cross-talk (NEXT), controlled ACR (attenuation minus cross-talk) and controlled shield transfer impedance.
One way twisted pair data cables have tried to meet the electrical characteristics, such as controlled NEXT, is by utilizing individually shielded twisted pairs (ISTP). These shields insulate each pair from NEXT. Data cables have also used very complex lay techniques to cancel E and B fields to control NEXT. Finally, previous data cables have tried to meet ACR requirements by utilizing very low dielectric constant insulations. The use of the above techniques to control electrical characteristics has problems.
Individual shielding is costly and complex to process. Individual shielding is highly susceptible to geometric instability during processing and use. In addition, the ground plane of individual shields, 360.degree. in ISTP's, lessens electrical stability.
Lay techniques are also complex, costly and susceptible to instability during processing and use.
Another problem with many data cables is their susceptibility to deformation during manufacture and use. Deformation of the cable's geometry, such as the shield, lessens electrical stability. Applicant's unique and novel high performance data cable meets the exacting specifications required of a high performance data cable while addressing the above problems.
This novel cable has an interior support with grooves. Each groove accommodates at least one signal transmission conductor. The signal transmission conductor can be a twisted pair conductor or a single conductor. The interior support provides needed structural stability during manufacture and use. The grooves also improve NEXT control by allowing for the easy spacing of the twisted pairs. The easy spacing lessens the need for complex and hard to control lay procedures and individual shielding.
The interior support allows for the use of a single overall foil shield having a much smaller ground plane than individual shields. The smaller ground plane improves electrical stability. For instance, the overall shield improves shield transfer impedance. The overall shield is also lighter, cheaper and easier to terminate than ISTP designs.
The interior support can have a first material and a different second material. The different second material forms the outer surface of the interior support and thus forms the surface defining the grooves. The second material is generally a foil shield and helps to control electricals between signal transmission conductors disposed in the grooves. The second material, foil shield, is used in addition to the previously mentioned overall shield.
This novel cable produces many other significant advantageous results such as:
improved impedance determination because of the ability to precisely place twisted pairs;
the ability to meet a positive ACR value from twisted pair to twisted pair with a cable that is no larger than an ISTP cable; and
an interior support which allows for a variety of twisted pair dimensions.
Previous cables have used supports designed for coaxial cables. The supports in these cables are designed to place the center conductor coaxially within the outer conductor. The supports of the coaxial designs are not directed towards accommodating signal transmission conductors. The slots in the coaxial support remain free of any conductor. The slots in the coaxial support are merely a side effect of the design's direction to center a conductor within an outer conductor with a minimal material cross section to reduce costs. In fact, one would really not even consider these coaxial cable supports in concurrence with twisted pair technology.